There are many theories as to the origin, nature, and best treatment of stuttering. Many speech pathologists believe that the root of stuttering is an inability to control the laryngeal muscles.
Speech sounds can be differentiated between voiceless sounds, such as /p/ and /t/, which are produced by the lips, tongue and jaw (the articulation muscles) altering the exhalation of air, and voiced sounds, such as /b/ and /d/, which are similar but also involve vibration of the larynx. This vibration is called phonation.
The larynx vibrates faster than the brain can control muscles--about 125-250 Hz. Phonation is caused by the vocal folds catching in air flowing past them. To phonate, the vocal folds must be neither too relaxed (allowing air to flow past without catching), nor too tense (blocking exhalation).
Most words contain both voiced and voiceless sounds, so a normal speaker will start and stop phonation many times per second. Persons who stutter have poor laryngeal control, usually tensing their vocal folds too tightly. Unable to move from a voiceless sound to a voiced sound, the person will repeat or prolong the voiceless sound ("c-c-c-c-cat"), or add an unrelated voiced sound to start phonation, ("ah, cat"), or not make any sound--a silent block. The person may try to push through the blocked larnyx by tensing neck or facial muscles.
The larynx is one of the first muscles people tense when experiencing fear or anxiety. Thus stuttering is often associated with fear and anxiety.
The most widely-practiced stuttering therapy is fluency-shaping therapy. A speech pathologist trains a person who stutters to:
Breathe with his diaphragm, which relaxes respiration muscles, and produces the gentle, steady airflow necessary for phonation. PA1 Gently increase vocal volume, and so laryngeal vibration, at the beginning of each phrase (gentle onset). PA1 Continue phonation through the end of the phrase, without stopping (continuousphonation), by keeping the vocal folds relaxed and air flowing. PA1 Speak slower, with prolonged vowel sounds, to enable continuous phonation (all vowels are voiced). PA1 Reduce articulatory pressure, by relaxing the lips, tongue, and jaw, and de-emphasizing voiceless consonants (produced by these articulation muscles) which interrupt phonation. PA1 1) the person never develops the target speech motor skills in the clinical environment; PA1 2) the person never transfers the target speech motor skills to his everyday life. PA1 1) Devices which enable immediate fluency, without training or mental effort. PA1 2) Motoric audition devices, which alter speech muscle activities by altering vocal perception. PA1 3) Biofeedback devices, which develop awareness and control of speech motor skills. PA1 1) Delayed auditory feedback (DAF) in the 25-75 ms range delays your voice (in your headphones) just long enough to overcome the stapedius muscle reflex, but is not so long that your voice is perceived as an echo. The device reduces stuttering 75-85%..sup.4 PA1 2) Frequency-altered auditory feedback (FAF) alters the pitch of your voice (in your headphones), typically 1/2 octave. The device reduces stuttering 75-85%..sup.5 PA1 3) Laryngeal auditory feedback (LAF) provides the sound of your larynx to your ears without the sounds added by your nasal and oral (tongue and lips) cavities. This can be accomplished in several ways. The Fluency Master (U.S. Pat. No. 4,784,115) tapes a microphone to your neck, and then amplifies your voice in a hearing-aid type amplifier. The device reduces stuttering in 30-80% of users..sup.6 The Edinburgh Masker (U.S. Pat. No. 3,566,858 and U.S. Pat. No. 3,773,032) electronically remove the sounds added by your nasal and oral cavities, providing only a sound similar to your laryngeal vibration. This device reduces or eliminates stuttering in about 90% of users..sup.7 PA1 Delayed auditory feedback (DAF) in the 125-250 ms range. You hear an echo of your voice in headphones. This forces you to prolong vowel sounds, and continuously vibrate your vocal folds (continuous phonation). This can completely eliminate stuttering. A 125-150 ms delay slows speech slightly, and sounds thoughtful and confident. A 150-250 ms delay slows speech considerably, and sounds robotic and monotonous. Long-delay DAF is useful in training the slow speech target in the clinic..sup.8 However, users refuse to talk abnormally slowly outside the clinic, so long-delay DAF has little value in transferring fluency. PA1 Metronomes can also help you prolong vowel sounds, similar to long-delay DAF..sup.9 PA1 A downward frequency-altered auditory feedback (FAF) shift slows down your speech slightly, and an upward pitch shift increases speaking rate slightly. These effects are too mild to produce carryover fluency. PA1 White noise masking auditory feedback (MAF) provides a random frequency noise to your ear, eliminating auditory perception. You then must talk by feel, and so improves proprioceptive awareness (the awareness of physical sensations of speech muscle activity). The device reduces stuttering moderately (about 35%), but requires volumes high enough to cause hearing damage..sup.10 PA1 Respiration can be monitored via a chest strap. PA1 Gentle onset devices, such as the Voice Monitor used in the Precision Fluency Shaping Program, train you to gradually increase vocal volume at the beginning of phrases, and maintain a constant volume through the end of the phrase. This is accomplished with continuous phonation. PA1 Vocal pitch biofeedack trains you to speak with a lower vocal pitch. You accomplish this with diaphragmatic breathing, slow speech, continuous phonation, and relaxed articulation muscles. PA1 Electromyographs (EMG) monitor muscle activity via electrodes taped to your neck and jaw. The device trains you to breathe with your diaphragm, speak slowly, continuously phonate, and talk with relaxed articulation muscles. Two studies of EMG stuttering therapy found a 40-70% long-term reduction in stuttering, after just 5-20 hours of therapy..sup.11 PA1 Electroglottographs measure vocal fold activity through electrodes taped to the neck..sup.12 PA1 Galvanic skin response (GSR) devices crudely measure general relaxation. Radio Shack sells a GSR biofeedback device for $15. PA1 Other devices monitor air velocity, tongue placement, nasality, etc..sup.13 PA1 The Visi-Pitch (Kay Elemetrics) is a computer-based system providing visual display of vocal pitch and amplitude. The system also provides delayed auditory feedback (DAF). The device includes measurement tools, statistical analysis, and video game visual feedback..sup.14 PA1 The Computer-Aided Fluency Establishment and Trainer (CAFET) combines a respiration monitor (chest strap) with vocal volume rate-of-change (gentle onset), to train seven fluency shaping skills. The system is computer-based. Visual feedback includes video games. Initially, both a graphical display of the your speech and text error messages are displayed. Then the graphical display is switched off, and only error messages appear. Lastly, no visual feedback is provided until the speech task is completed, and then error messages are displayed. This trains you to talk fluently after discontinuing use of the device. One study found that 92% of users were fluent two years after completing the therapy program..sup.15 PA1 The Biofeedback System For Speech Disorders (made by Casa Futura Technologies, of Monte Sereno, Calif., patent application Ser. No. 08/216,630, filed Mar. 22, 1994) bridges the gap between the effective but large and expensive clinical devices (such as the Visi-Pitch and CAFET) and the small, affordable, but too often ineffective consumer devices (such as the Fluency Master and Edinburgh Masker). The device is portable, providing DAF, FAF, and EMG biofeedback. When the device detects stuttering, it switches on DAF. If it detects severe stuttering, it alters the DAF pitch, providing FAF. When the device detects on-target fluent speech, it switches off auditory feedback. As you develop your fluency shaping motor skills, the device automatically switches itself off, until you no longer need to use the device. The device also plugs into telephones.
Fluency-shaping therapy begins by teaching these speech motor skills in the clinical environment. The speech pathologist models the behavior, and provides verbal feedback as the person learns to perform the motor skill.
At first, the target speech behaviors are exagerated, producing abnormally slow, monotonous, but relaxed and fluent speech. As the person develops speech motor control, he increases rate and prosody until his speech sounds normal.
When the person's speech is fluent and sounds normal in the clinical environment, he works with the speech pathologist the transfer these speech motor skills to his everyday life.
Fluency-shaping stuttering therapy is effective for about 70-75% of adults who stutter (and more effective for children who stutter), according to recent research.sup.1.
 FNT .sup.1 Boberg, E., Kullyn D., "Long-Term Results of an Intensive Treatment Program for Adults and Adolescents Who Stutter," Journal of Speech and Hearing Research; October 1994, 37(5)
There are two broad reasons for the failure of fluency-shaping stuttering therapy:
A variety of electronic devices are available to aid both of these goals. Electronic devices can also reduce the fear and anxiety associated with stuttering.
These electronic devices can be divided into three main classes: